Abstract: Selective protein kinase inhibitors are powerful tools for interrogating cellular signaling pathways and validating drug targets for the treatment of a variety of cancers. The drug discovery paradigm that exists today starts with the identification and validation of kinase targets primarily at academic institutions followed by inhibitor development by the pharmaceutical sector. A major shortcoming of this paradigm is the severe shortage of selective inhibitors for most kinases hampers initial pharmacological proof-of-concept studies and therefore discourages further exploration of these targets by the pharmaceutical sector. Our laboratory has attempted to address this deficiency by developing efficient approaches to the discovery of first-in-class kinase inhibitors, which are then used as pharmacological 'tools' to investigate the functions and potential therapeutic relevance of the kinase in question. Over the last five years, our laboratory has developed and widely distributed the first inhibitors of ALK, Mps1, Erk5, mTor, LRRK2, FGFRs, JNKs, and the T790M mutant form of EGFR; several of which are currently standard reference compounds. In this application we have assembled a multidisciplinary team that integrates medicinal chemistry (Nathanael Gray), structural biology (Jane Endicott), transcription (Richard Young) and cancer biology and translational research (Constantine Mitsiades) that will enable the development and application of the first highly potent and selective inhibitors of CDK7. The cyclin-dependent kinases are a highly conserved class of protein kinases that consist of 20 members (CDK1-20) that associate with a family of 29 regulatory proteins called cyclins. They regulate a large number of cellular functions including cell cycle (CDK1-6), transcription (CDK7-13, 19), and splicing (CDK11). While the cell cycle regulating CDKs have received a significant amount of attention as drug discovery targets the so-called 'transcriptional CDKs' (tCDKs - CDK7-13, 19) have received much less. We have discovered an unprecedented means of developing selective CDK7 inhibitors by covalently targeting a unique cysteine (Cys) residue located outside of the kinase domain. We have obtained compelling preliminary data of the activity of CDK7 inhibitors in a large number of cancers, but here we propose to focus on investigating the potential of targeting CDK7 for the treatment of Multiple Myeloma, a plasma cell tumor where excess transcription is a hallmark of the disease and, based on our preliminary data, CDK7 plays a critical pathophysiological role. This will be accomplished through a focused medicinal chemistry campaign (Aim 1) and guided by detailed mechanistic characterization (Aim 2), followed by preclinical evaluation in cellular and murine models of Multiple Myeloma (Aim 3).